International Concrete Abstracts Portal

The role of concrete in the corrosion of steel in reinforced concrete has received a considerable amount of attention in recent years. This is due to the recognition of the strong relationship between the nature of the concrete and its ability to protect embedded steel. Therefore, in addition to some of the commonly used corrosion protection methods that focus on either coating the concrete, increasing the cover of the concrete, coating the reinforcing steel, or the use of inhibitors that change the nature of the surface of the reinforcing steel, other methods should be included that emphasize the role of the concrete mix design. Paper deals with the contribution of concrete to the corrosion of reinforcing steels in reinforced concrete. Twenty-six mix designs that represent concretes that could be used today were selected for study. Variables included cement content, water content, amount and type of fly ash, the addition of superplasticizers, and air entrainment. Strength and macrocell current were measured as a function of chloride exposure. The results of 1 year of cyclical exposure to 3.5 percent NaCl solution revealed that the concrete influences the corrosion process greatly. Furthermore, modification of concrete can become another method of corrosion protection through a better understanding of the relationship between the corrosion process and concrete mix design.

The service life of latex-modified concrete and low-slump dense concrete bridge deck overlays is estimated by extrapolating historical performance data obtained from the results of field research and investigations conducted in the U.S. and Canada. The data suggest that when concrete removal criteria are based on half-cell potential rather than actual damage, when removal of chloride-contaminated concrete is extended to below the reinforcing bar, and when the substrate is sandblasted to remove microcracking prior to cleaning, a mean service life of 30 to 50 years is likely.

On-site monitoring of the rate of corrosion of reinforcements is a priority task. There are various available devices for measuring I corr. Most of them entail a prior measurement of the {DELTA}E/{DELTA}I, which defines the polarization resistance (R p). However, direct estimations of R p from the {DELTA}E/{DELTA}I ratio are usually unfeasible with large structures because they provide an apparent polarization resistance (R p app) that differs to a greater or lesser extent from the true R p value depending on the experimental conditions. This paper analyzes the influence of some experimental factors (that is, the use of unconfined or guard ring-confined electric signals, the CE size, and the presence of active and passive areas in reinforcements) on the R p app accuracy of the I corr values derived from it. The more correct I corr values can be obtained by sensorized confinement of the electric signal applied with the aid of a guard ring and supplementary reference electrodes for monitoring the electric field confinement.

The practice of prestressing steel has proven to be a very successful method of construction compared to conventional reinforced concrete in increasing load-carrying capacity, improving crack control, and slenderizing structural elements. However, corrosion in prestressed concrete has much more serious consequences than in normal reinforced concrete. Tendons are subjected to high mechanical stresses (often up to 70 to 80 percent of their tensile strength). Under an FHWA contract dealing with rehabilitation of prestressed concrete bridge components by nonelectrical methods, a comprehensive technology review focusing on corrosion of prestressing steel in highway structures was conducted and is summarized in this paper. Types of corrosion and recent theories explaining stress corrosion and hydrogen embrittlement are presented. Susceptibility of prestressing steel to corrosion in prestressed and post-tensioned concrete structures is covered. Factors such as concrete materials, prestressing steel, and environments, which may influence such corrosion, are categorized. Laboratory and field studies dealing with a variety of corrosion issues in pretensioned and post-tensioned concrete are also presented. These issues include the development and improvement of grout materials for bonded tendons in post-tensioned concrete members, use of epoxy-coated prestressing wires, and corrosion of unbonded tendons under severe exposure. Selected case histories and field evaluation of concrete bridges subjected to corrosion are also included. This study gives an overview of corrosion problems in prestressed concrete members and should help engineers to diagnose causes of corrosion and select the right methods and materials to be used for rehabilitation as well as in new constructions.

Calcium nitrite corrosion inhibitor has been commercially available in the U.S. since 1978. In that period of time, over 200 parking structures, 100 marine structures, and more than 230,000 m 3 (300,000 yd 3) of precast/prestressed bridge girders have been constructed with concrete containing calcium nitrite. In this paper, several of the oldest structures, along with several test sites, were evaluated to determine the corrosion performance. The condition assessment included a visual evaluation of the structure, determination of chloride and nitrite contents in the concretes, and determination of the corrosion activity. The corrosion tests consisted of corrosion potential mapping and polarization resistance testing to determine the corrosion rates at the time of the evaluation. These assessment techniques are applicable to all steel reinforced concrete structures with or without some modifications. The assessment showed that all of the structures with calcium nitrite are performing well. In two cases, there is evidence that corrosion is in progress on adjacent structures that were not protected with calcium nitrite. The nitrite analyses document that calcium nitrite is stable in concrete and remains at the reinforcing bars. Diffusion of chloride is not increased in the concretes with calcium nitrite, and there is evidence of a reduction in chloride penetration in some cases.